Congress has approved a 10-year extension on the ban on plastic weapon (specifically, weapons that can evade metal detectors). With increased access to 3D printing, there is concern that such guns might become prevalent. The law is set to expire tonight, December 9, at midnight.

President Barack Obama, however, is flying to South Africa to attend the funeral of Nelson Mandela. The White House has indicated that Mr. Obama will sign the bill with an "autopen."

Professor Terry Turnipseed has written on the use of the autopen. (And this is not unprecedented: see, for instance, discussion from Professor Josh Blackman on the matter.) Even though there are memoranda from the Department of Justice indicating it is constitutional, Professor Turnipseed makes a persuasive that the use of the use of the autopen is not a constitutional alternative to an actual signature. [UPDATE: This is a close question for me--I think Professor Turnipseed makes a persuasive case, but I could be persuaded otherwise. Accordingly, this post is an exercise based upon the assumption he is correct.]

The consequence, then, is that the bill is unsigned, and after 10 days (excluding Sundays), one of two things happen. If Congress is in session, the bill becomes law. If Congress is not in session, the bill is vetoed, known as a "pocket veto."

In most cases, Professor Turnipseed notes, it means that the law is not in effect for 10 days, and it usually becomes law after that. Most of the time, the law simply has not taken effect, or it lapses until the end of the 10 days.

But Congress has indicated that it would adjourn December 20. Ten days (excepting Sundays) take us through the end of December 20. So after midnight, we arrive at December 21, and we see that Congress is not session. And that means that the law has been vetoed.

This, of course, assumes that someone challenges the law (perhaps after arrest), and that a court accepts the argument that the law was vetoed because the use of the autopen was unconstitutional.

But there is one option at Mr. Obama's disposal. Article I, section 7 reads that the law takes effect after 10 days, "unless the Congress by their Adjournment prevent its return, in which case it shall not be a Law."

The Senate may wellhold pro forma sessions after the intended recess on December 20.

Which means that Mr. Obama would be placed in the interesting position of defending the validity of the law after that date by arguing that the pro forma meetings of Congress mean that it has not entered into recess between sessions. Which would place him at odds with his position in the Noel Canning case. (There's a great deal more subtlety in the constitutional interpretation in the recess appointments cases, of course.)

It's deeply, deeply unlikely, I suppose... but it's the convergence of factors that makes this problem so interesting (to me, at least!).